Various respiratory aids are now widely available to a subject wishing to self-administer therapeutic and preventative agents to combat the symptoms of a respiratory disorder such as asthma. These aids come in a range of shapes and sizes to suit the age and ability of the subject. Such respiratory aids include inhalers and auxiliary devices such as spacers, optimisation chambers, reservoirs, expansion chambers and deceleration chambers.
A common example of a respiratory aid is the inhaler which is a manually operated device used to dispense into the respiratory passages a discrete amount of a therapeutic or preventative agent (e.g., in the form of a spray). One of the benefits of an inhaler is that the subject is able to manage the respiratory disorder through self-administration of a preventative agent. A successful preventative regime relies on regular self-administration of the preventative agent to avert breathing difficulties and other respiratory symptoms. Breathing difficulties may occur suddenly and indiscriminately and their onset frequently leads to a loss in co-ordination. A second benefit of an inhaler is that sudden respiratory attacks may be treated by immediate self-administration of the desired therapeutic agent. The preventative and therapeutic benefits of the inhaler rely on the subject being able to locate reliably and effortlessly an inhaler with an at least partially charged container.
In principle inhalers are available in two types, namely an aerosol device powered by a propellant (e.g., a metered dose inhaler of the type described in inter alia GB-A-2293110) or a powder containing device (e.g., a metered dose powder inhaler). The therapeutic or preventative agent may be in dry powder or liquid (e.g., suspension) form and generally speaking is drawn into the respiratory passages by simultaneously dispensing the agent and taking a sharp intake of breath.
Most forms of aerosol inhaler comprise a metal container for the therapeutic or preventative agent and a discharge valve through which the agent may be dispensed continuously or discretely via a nozzle. For example, conventional metered dose inhalers comprise a metal canister secured to a metered dose valve. A determination of the number of doses remaining in the canister requires a manual record of the number of doses which have been dispensed (for example using a mechanical counter). Many counter devices of a mechanical type have been proposed.
U.S. Pat. No. 3,505,870 discloses a metal aerosol container with a transparent window in a small circular opening in the base.